This invention relates to the metallization of support members and, more particularly, to the metallization of cellulosic support members such as paper.
Metallization is a process in which a metallic material, such as aluminum, is applied to an underlying support member. This can be done by bonding a thin film of metallic foil to the surface of the support member. The bonding takes place using a suitable adhesive and the resulting product is a laminate of the support material and the foil.
Alternatively, metal is vaporized in a high vacuum using resistance, induction or an electron beam and forms a metallic layer on a support member. This procedure is suitable only for support members that do not contain significant amounts of moisture. When moisture is present, the vacuum draws vapors and other by-products which must be eliminated before subsequent metallizing can take place. Irregularities in the support surface also appear in the final product.
As a result, where it is desired to employ a vacuum for the direct metallization of a paper support member, the paper is first dried to a level where there will be negligible outgassing. This procedure, however, makes the support material brittle and difficult to process. Additionally, once the vacuum metallization of the dried paper is completed, it is necessary to restore its moisture level to near its original value. This is a time consuming and costly procedure that requires the use of appreciable amounts of energy for drying.
Accordingly it is an object of the invention to facilitate the metallization of support members, particularly cellulosic products such as paper. A related object is to facilitate the metallization of support members with irregular surfaces. Another related object is to achieve suitable metallization of support members that exhibit outgassing when subjected to a vacuum.
Another object of the invention is to achieve suitable smoothness and reflectivity for metallized support surfaces.
Still another object of the invention is to achieve efficient and high speed metallization of support members.
Still other objects of the invention are to overcome the disadvantages associated with metallization by foil lamination and metallization by vacuum.
One attempt to overcome the foregoing difficulties involves the application of an adhesive with dispersed metallic powder to a support surface. This procedure requires that the metallic laden adhesive be allowed to cure on the support surface. Curing requires that the product be aged for a considerable period of time. The result is a reduction in the efficiency and speed with which the desired metallized product can be produced. Furthermore, metallic powder creates environmental dust objections. There can be the further objection that surface irregularities in the support member are not completely compensated. Finally the dispersion of metallic powder in an adhesive prevents the realization of a continuous metallic film and is accompanied by an inevitable reduction in the reflectivity of the metallized surface. Much of the metal is deposited at an internal level of the adhesive where it is ineffective in the desired reflectance of light.
Accordingly it is still another object of the invention to achieve suitable metallization of support members having irregular surfaces without the disadvantages associated with the prior art use of metallic powders.
Another object is to achieve the desired metallization without requiring that metallic powder be dispersed in an adhesive which must be allowed to cure.
Still another object of the invention is to increase the efficiency of metallization over and above that which can be achieved by a process which requires curing.
A further object of the invention is to increase the efficiency with which the metal used in metallization contributes to the reflectivity of light from a metallized surface. A related object is to avoid the loss of reflectivity by metallic elements such as powder which becomes embedded below the surface where the reflectivity takes place.